Although human beings naturally perceive three dimensions through stereoscopic vision, most electronic images are formed on two-dimensional display screens. Commercial television, for instance, is 2-D. Many advantages are to be gained from techniques for perceiving three dimensions from a two-dimensional screen, including the enhanced understanding of technical displays, and the increased enjoyment of programming intended for entertainment purposes.
Various techniques are understood and available to provide true three-dimensional viewing through a two-dimensional display screen. A straightforward approach is to record the image to be viewed through two lenses, and provide the viewer with glasses incorporating electro-optical shutters which selectively present only one perspective to each eye, thereby recreating depth perception in accordance with the vantage used for the original recording. Electronically synchronized liquid-crystal shutters are often used in the viewing glasses associated with such systems.
Other genuine three-dimensional viewing techniques are possible. However, in all cases, to realize true three-dimensionality, stereoscopic recording must be employed. As such, a duplication of hardware, including separate recording, storage and display means must necessarily be provided in order to accommodate faithful reproduction of the different perspectives delivered to the two eyes of the viewer. This complication not only results in increased equipment, but also requires in more sophisticated system overall, involving alignment, synchronization and increased bandwidth requirements for transmission and display, as in the case of true 3-D television. To implement such systems on a large scale basis would require fundamental changes to the infastructure now used for television broadcasting, as well as alterations to the media now used for video and/or film recording.
The added cost and complexity of true 3-D imaging has led to the desire to develop illusionary or pseudo-stereoscopic techniques and systems which, broadly speaking, manipulate a monocular or two-dimensional image in such a way that an illusion of three-dimensionality is perceived by the viewer. These systems represent a compromise between providing all of the necessary hardware and control required for true 3-D, but require the viewer to synthesize three dimensions, when, in fact, only two-dimensional information is provided. Such systems may split the two-dimensional image into two temporally offset versions of the image then, using glasses with special lenses, force each eye to see only one of the offset images. Horizontally displaced images are most effective, since human eyes are naturally horizontally displaced.
With true three-dimensional perception, the separation of the eyes of the viewer introduces parallax into the observed scene. Part of the parallax contribution results in an offset of one image relative to the other such that an object at the center of the scene will be displaced to the right of the center for the left eye and to the left of the center for the right eye. Various degrees of horizontal offset will occur at various distances such that closer objects will be more offset than objects which are further away.
In contrast, a two-dimensional image does not contain offset information as described above. An artificial offset may, however, be introduced by simultaneously presenting an identical image in two slightly different horizontal positions to both eyes. Such a technique, if properly applied, causes the eye muscles to converge at a plane in space which is different from the true plane of projection, resulting in an image which is perceived to be three-dimensional.
To create such a pseudo-stereoscopic image electronic means may be employed. For example, in my copending parent application, I describe an electronic module which is operatively connected between an incoming signal source and a display device, the module performing horizontal delay and scan adjustments to alternating fields of the television image. Vertical size and luminance may be modified as well to further enhance the perception of three-dimensionality. A pair of liquid-crystal glasses operatively communicate with the module to force each eye to perceive only one of the alternating field.
Electronic means are effective in modifying a 2-D image so as to achieve an illusion of three dimensionality, but such an "active" approach adds significantly to the sophistication of the image viewing apparatus. Although a scene need not be recorded in 3-D, the circuitry required to adjust horizontal and vertical dimensions and brightness, is nevertheless complex, and, although these functions may be performed external to the television receiver, the greatest advantage is realized by performing such functions internal to the television receiver, thus increasing the sophistication and cost of a consumer item. Whether recorded three-dimensionally or synthesized, active approaches which alternate between eyes further introduce at least some degree of "flicker" due to the refresh period, approximately 60 Hz with NTSC, as well as any refresh-related harmonics which are present.
Therefore, although such electronics-intensive pseudo-stereoscopic systems are available for creating three-dimensionality in a 2-D image, the circuitry involved may be beyond the means of a large class of consumers. If a less complex approach were available to derive geometrically offset versions of a two-dimensional image, it may present an advantage in terms of affordability and reliability. In the case of projection television, such a simplified system would ideally be compatible with color images associated with either a single projection lens or multiple projection lenses.